To stay alive, pharmaceutical companies have to continually develop new drugs to replace the ones that go off patent. But the amount they spend on research and development relative to their revenue varies widely, with Merck (MRK -0.64%), AstraZeneca (AZN -0.67%), Roche (RHHBY 1.26%), Bristol-Myers Squibb (BMY -2.19%), and Eli Lilly (LLY 1.85%) topping the chart.

Unfortunately, with long development cycles, we won't know for a few years whether the extra dollars being thrown into research and development now will ultimately benefit the companies. In the slide show below, find out more about the reasons behind the companies shelling out so much cash to develop new drugs.

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